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BREATHER MEMBRANES FOR WOOD FRAME WALLS

A breather membrane is a water-resistant material which will allow water vapour to pass through
when there is a difference in humidity on opposite sides of it. Breather membranes are used on the
outside of frame walls under the exterior finish material. They have three functions to perform:

1) to shed moisture and restrict any rain water which penetrates past the exterior finish from reaching
the wood wall,

2) to perform as a breather material allowing any moisture within the wall cavity to escape by
diffusion through the membrane to the exterior, and

3) to act as a wind barrier to restrict movement of air through the wall.

To qualify for the above functions the breather membrane must have good "water resistance", good
"water vapour permeability", and good "air barrier properties". All of these properties can be measured
in a laboratory, and building codes require minimum levels of performance. The Canadian standard
for breather membranes is CAN 2-51.32 and the U.S. standard is UUB-790a.

Water Vapour Permeability: Canadian Standard CAN 2-51.32 requires a water vapour permeance of
2.0 (minimum) to 16.5 (maximum) metric perms when tested according to ASTM E 96-90. One
metric perm is equivalent to 87 nanograms/Pascal, second, sq. meter (ng/Pa.sec.m2).

Water Resistance: U.S. Standard UUB-790a requires a minimum water resistance rating of 10
minutes for grade D breather paper when tested according to UU-P 31b (ASTM 779). Although the
National Building Code of Canada does not set test standards for this, some localized jurisdictions
require 30 minute or 60 minute ratings. (Water resistance is a measure of the time it takes for
sufficient dampness to permeate through a material to cause an indicator dye on its surface to turn
colour when the opposite side of the material is in contact with water).

Air Barrier Performance: There are no specific air-barrier standards set for breather membranes in
the National Building Code however wall assemblies must meet the requirements of Section 5.4 "Air
Leakage". As a component in the wall system, the breather membrane should contribute to the overall
wall performance. Air-barrier performance values are shown below for various products.

Discussion
Breather membranes are intended to function as a secondary protective layer beneath the external wall
cladding. High winds or capillary forces can sometimes cause moisture to seep behind the wall
cladding during rainy periods. This moisture will reach the breather sheet and migrate downwards on
its surface. The breather sheet is intended to prevent this moisture from reaching the wood wall
sheathing, however because most cladding is attached with nails or screws which penetrate the
breather sheet, moisture can sometimes pass through at these penetrations and reach the wood
sheathing, especially if there is a wind-induced pressure differential in the wall assembly. Moisture
can also pass through as a vapour if it is held trapped against the breather sheet for long periods of
time.

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Once moisture reaches the wood sheathing it can cause wood rot to occur, especially when the exterior
cladding is a type which restricts the rate of drying. With present day construction methods, walls do
not easily dry inwards, so moisture must dry externally through the cladding. Cladding which is
continuous and has no gap between it and the wall sheathing will be the most restrictive to rapid wall
drying (eg: stucco or panel-type cladding).

Preventing Water Damage to Frame Walls

The following are some suggestions:

1) Always use TWO LAYERS of Breather Membrane. The outer layer of paper can become damp
from wet cladding; however the inner layer keeps the wood wall separated from direct contact with
this dampness. The outer layer can take the abuses of numerous wet and dry cycles in the wall,
while the inner layer remains unaffected over time.

Two layers, when tested in the water resistance test, achieve a result of greater than 2.5 hours,
compared to 30 – 45 minutes that 1 layer of 30 Minute building paper achieves.

2) Create a DRAINAGE CAVITY between the cladding and wall sheathing. (RAINSCREEN
Construction) The National Building Code of Canada (N.B.C.) states that 'drainage is required'
when a wall assembly may be penetrated by moisture (Par A-5-6.2.1). The B.C. Building Code in
paragraph 5.4.5.1 states that 'Where there is a likelihood of some penetration, drainage shall be
provided to take water to the outside.' Some jurisdictions have enacted laws requiring that a cavity
be built behind certain types of cladding (eg: Vancouver, B.C. for multi-unit buildings).

A drainage cavity can be created by using vertical wood strapping nailed to the wall over the
breather membrane. Cladding is then installed over the wood strapping usually over a second
backing sheet. HAL-TEX RAINBOARD can be used as a backing for stucco over vertical
strapping since it is rigid enough to span between spaced supports.

Architects, Building Envelope consultants and concerned builders are becoming very cognizant of the
need to protect wall structures from water damage. The suggestions given above and the products
listed below are intended to help achieve these goals.

 HAL-TEX "30 MINUTE" Building Paper: A medium-weight asphalt saturated kraft paper with
good strength and pliability which meets the 30 minute water resistance test. This product is
suitable for general purpose use. May be used in a single ply or double ply application under
wood, metal, vinyl or stucco siding. Meets CAN 2-51.32 and U.S. Standard UUB-790a.

Product Weight: 4.13 lb/100 ft2

Tensile Strength: >5.7 N/ mm
Water Vapour Permeability (1ply): 420 ng/ Pa. sec. m2 (4.8 metric Perms)
Water Resistance Rating (1-ply): 30 - 45 minutes
Water Resistance Rating (2-plies): >2.0 Hours
Air Barrier Rating @ 100 Pa: 0.175 L/m2, sec. 1-ply
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 HAL-TEX "60 MINUTE" Building Paper: A heavy-duty asphalt saturated kraft paper with
superior strength and extra thickness. Meets or exceeds 60 minutes of water resistance. This
product is suitable for use as a breather membrane where a higher degree of moisture protection is
desired. May be used under stucco or other types of siding in a 1-ply or 2-ply application. Meets
CAN 2-51.32 and U.S. Standard UUB-790a.

Product Weight: 7 lb/ 100 ft2

Tensile Strength: >7 N/ mm
Water Vapour Permeability: 320 ng/ Pa. sec. m2 (3.6 metric Perms)
Water Resistance Rating: 60 - 90 minutes
Air Barrier Rating @100 Pa: 0.120 L/m2, sec. 1-ply

 HAL-TEX RAINBOARD: is a three ply laminated board made up of a corrugated asphalt kraft building
paper at its centre and faced on each side with asphalt-kraft building paper. The innovative method of its
production and lamination results in the creation of a semi-rigid lightweight board, which is water-resistant,
but permeable to water vapour. HAL-TEX RAINBOARD meets the intent of the CAN/CGSB 51.32 and
UU-B-790a standards for breathable sheathing membranes for frame walls. HAL-TEX RAINBOARD
represents a major step forward in outer wall protection. It provides separation, and drainage capability
between the outer wall cladding and the moisture sensitive wall structure for better moisture
protection.

HAL-TEX RAINBOARD is designed for use on walls directly over exterior wall sheathing or furring
strips. Suitable for use beneath most types of outer wall claddings such as stucco, stone, Hardi board, etc.
For rainscreen walls the furring should coincide with stud positions with a mid span backer strip to keep
board flat.

Width x Length: 1 meter (40”) nom. x 1.62 meter (64”) nom.

Thickness: nominal 2.9 mm (B flute) and 3.8 mm (C flute).
Tensile Strength M Dir.: 610 N/25.4mm (137 lbf/linear inch) ASTM D828
Tensile Strength C Dir.: 442 N/25.4mm (99 lbf/linear inch) ASTM D828
Water Vapour Permeance: 392 ng/Pa.sec.m2 (ASTM E96 Dry Method)
After Accelerated Aging: 835 ng/Pa.sec.m2 (ASTM E96 Dry Method)
Diffusion Water Resistance: > 5 hrs. (UUB-790a Indicator method with one side wet)

 HAL-TEX "CORPLY”: Is a two-ply breather-type asphalt kraft Building Paper which has one
corrugated ply laminated to one smooth ply. This product is intended for use on building walls
beneath the external finish as a self-draining building envelope material. The corrugated-ply
provides vertical channels for a capillary break and a secondary drainage plane for incidental
moisture. Listed under CCMC Listing # 11479-L for building paper used as sheathing
membranes. COR-PLY is intended for use in regions where a full rainscreen cavity (10 mm) is not
a code requirement, but where better moisture protection for walls is desired.

Intended for use on walls beneath stucco, stone or other types of wall finish where a separating air
gap is desired between the structural wall surface and the external finish. COR-PLY combines
three very effective ways to keep a wall dry:

1. PHYSICAL SEPARATION of the outer wall finish from the wall sheathing to reduce moisture
ingress by capillary action or wicking.
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2. DRAINAGE PATHWAYS for improved downward flow of any moisture which may bypass
the outer wall finish through incidental points of entry, and

3. EASIER VAPOUR RELEASE from behind the wall cladding via channels vented to the
atmosphere.

Width: 1 m (40") nom., 36" coverage.

Thickness: 3.5 mm nom.
Sheet Size & Coverage: 1m x 10 m nom. coverage/roll = 36" x 32.5' (100 ft2)
& - 1m x 2 m nom. coverage/sheet = 36" x 80" (20 ft2) -
100 sheets/ box
Water Vapour Permeance: > 3.0 metric perms 264 ng/ Pa.sec m2 (ASTM E96)
Compliance: CAN 2-51.32 M77, CCMC Listing # 11479-L

The information presented herein, while not guaranteed, is to the best of our knowledge true and accurate. Except when
agreed to in writing for specific conditions of use, no warranty or guarantee expressed or implied is made regarding the
performance of any product, since the manner of use and handling are beyond our control. The user of such information
assumes all risk connected with the use thereof. Nothing contained herein is to be construed as permission or as a
recommendation to infringe any patent.
Revised 9, Mar 2012 BreatherMembranes_WoodFrameWalls.doc